Method and apparatus for filling a gap between spaced layers of a semiconductor

ABSTRACT

A semiconductor device assembly with a gap to be filled has thermal vias formed in the supporting substrate. After the semiconductor device is connected to the substrate and fill material positioned about the gap to create a seal, a vacuum is drawn through the thermal vias and a pressure applied to the fill material to urge the fill material into the interior of the gap.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/185,446,filed Oct. 29, 1998, now U.S. Pat. No. 6,232,145 which is a continuationof application Ser. No. 08/789,269, filed Jan. 28, 1997, now U.S. Pat.No. 5,866,442, issued Feb. 2, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for underfilling thegap between a semiconductor device mounted on a substrate, such as aflip chip semiconductor device mounted on a substrate.

2. State of the Art

A flip chip semiconductor device mounted on a substrate is one type ofarrangement having a gap formed between the flip chip semiconductordevice and the substrate. A semiconductor device is said to be a “flipchip” because it is manufactured in wafer form having its active surfacehaving, in turn, bond pads thereon initially facing upwardly. Aftermanufacture is completed and the semiconductor device singulated fromthe wafer, it is “flipped” over such that the active interior surfacefaces downwardly for attachment to a substrate. For attachment to asubstrate a flip chip semiconductor device is formed having bumps on thebond pads of the active surface thereof which are used as electrical andmechanical connectors with the substrate. Several materials may be usedto form the bumps on the flip chip semiconductor device, such as varioustypes of solder and alloys thereof, conductive polymers, etc. Inapplications using solder bumps, the solder bumps are reflowed to form asolder joint between the flip chip semiconductor device and thesubstrate. The solder joint thereby forming both the electrical andmechanical connections between the semiconductor device and thesubstrate. Because of the presence of the bumps, a gap is formed betweenthe semiconductor device and the substrate.

Since the semiconductor device and the substrate are typically formed ofdiffering materials, the semiconductor device and the substrate havedifferent mechanical properties with differing attendant reactions tooperating conditions and mechanical loading thereby causing stress todevelop in the bumps connecting the semiconductor device to thesubstrate. Therefore, the bumps are typically made of sufficient robustsize to withstand such anticipated stressful conditions thereby causinga substantial gap to be created between the semiconductor device and thesubstrate. To enhance the joint integrity between the semiconductordevice and the substrate a fill material is introduced into the gaptherebetween. The fill material, called an underfill material, helpsequalize stress placed on the solder bumps, the semiconductor device,and the substrate as well as helping to insure that the bumps and otherelectrical features of the semiconductor device and the substrate bemaintained free from contaminants, including moisture, chemicals,chemical ions, etc.

In some applications, the fill material is typically dispensed into thegap between the semiconductor device and the substrate by injecting thefill material along one, two, or more sides with the underfill materialflowing, usually by capillary action, to fill the gap. For example, U.S.Pat. No. 5,218,234 (Thompson et al.) discloses a semiconductor deviceassembly where an epoxy fill material is injected around the perimeterof the chip mated on the substrate. The epoxy material has a viscositypermitting it to flow into the gap. A hole may be provided in thesubstrate to facilitate positioning the material into the gap.

It has been noted that underfilling the gap by way of capillary actionmay lead to non-uniform disposition of the fill material within the gap.Typically, the fill material may have bubbles, air pockets or voids.Non-uniform disposition of the material in the gap decreases the fillmaterial's ability to protect the interconnections between thesemiconductor device and the substrate and may lead to a reduction inthe reliability of the semiconductor device.

In some arrangements, such as those disclosed in U.S. Pat. No. 5,410,181(Zollo et al.), a hole in the substrate is provided through which accessmay be had to the circuit for performing various operations thereon,including optical operations associated with the circuit. A plug ispositioned in the hole which precludes positioning the fill material inthe area associated with the plug. That is, the fill material isinserted with the plug in place in the hole.

U.S. Pat. No. 5,385,869 (Liu et al.) discloses a device in which a gapbetween the semiconductor device and the substrate is underfilled byforming a large hole through the substrate. The hole may even have gatesor notches formed at each corner which extend beyond the hole. Theunderfill material flows through the hole by way of the gates or notchesin the substrate in order to facilitate complete underfilling.

U.S. Pat. No. 5,203,076 (Banerji et al.) teaches one to apply a vacuumto evacuate air from the gap between the chip and the substrate. Air isthen slowly allowed to reenter the vacuum to force the underfillmaterial into the gap between the semiconductor device and thesubstrate.

Underfilling may also be seen in the manufacture of semiconductordevices illustrated in U.S. Pat. No. 5,371,404 (Juskey et al.), U.S.Pat. No. 5,258,648 (Lin), U.S. Pat. No. 5,311,059 (Baneiji et al.) andU.S. Pat. No. 5,438,219 (Kotzan et al.).

As previously stated, semiconductor devices that are underfilled orfilled with a material in the gap between the semiconductor device andthe supporting substrate frequently encounter non-uniform disposition ofthe fill material. Therefore, improved underfilling methods that improvethe quality of the underfilling of the gap between the flip chip typesemiconductor device and the substrate, that are cost effective, andthat use improved and lower cost fill materials are desired.

BRIEF SUMMARY OF THE INVENTION

In a preferred arrangement of the invention, a semiconductor deviceassembly includes a flip chip semiconductor device and a substratehaving a plurality of thermal vias therein. The flip chip semiconductordevice has a first exterior surface and a second active interior surfacehaving, in turn, bond pads thereon including solder bumps thereon aselectrical and mechanical interconnection structure. The substratecomprises a substrate having a metallized surface pattern of electricalcircuits thereon for connection with the interconnection structure of aflip chip semiconductor device and a plurality of thermal vias extendingtherethrough. After the interconnection structure of the flip chipsemiconductor device is connected to portions of the metallized surfaceof the substrate, a fill material is used to fill the gap between theflip chip semiconductor device and the substrate by applying a vacuumthrough the thermal vias in the substrate and, if desired, fluidpressure to the fill material. Preferably the fill material includes afiller.

A method of making a semiconductor device assembly comprises providing asemiconductor device having a first surface and a second active interiorsurface. The second active interior surface has one or more bond padsthereon which has, in turn, electrical interconnection structure formedthereon and extending therefrom. A substrate includes one side thereofhaving a metallized surface pattern of electrical circuits thereon forcontact with the electrical interconnection structure of the bond padsof the semiconductor device and another exterior surface spaced from themetallized surface. A plurality of thermal vias extends through thesubstrate from the metallized surface to the other exterior surface. Thethermal vias are sized and configured for heat transfer from the gapadjacent the metallized surface of the substrate to the other exteriorsurface of the substrate. The semiconductor device is connected toportions of the metallized surface of the substrate having theelectrical interconnection structure of the bond pads of thesemiconductor device contacting the desired portions of the metallizedsurface of the substrate, thereby forming a gap having a perimetertherebetween. Fill material is positioned proximate at least a portionof the perimeter of the gap between the metallized surface and thesecond surface of the semiconductor device. A source of vacuum ispositioned proximate the exterior surface of the substrate relative tothe thermal vias to draw a vacuum through the thermal vias to urge thefill material into the gap.

If desired, a source of pressure may be provided and positioned to applypressure against the fill material, in addition to the vacuum, tofurther urge the fill material into the gap.

Preferably, the electrical interconnection structure is a plurality ofbumps formed on the second active surface of the semiconductor device.The fill material may include suitable fillers in combination withsuitable electrical insulating material. The thermal vias may betypically sized in diameter from 0.001 inches to 0.010 inches.

The present invention also includes apparatus for filling the gapbetween a semiconductor device and a substrate of a semiconductor deviceassembly. The apparatus includes a supporting structure to support thesemiconductor device assembly. The semiconductor device assembly has afirst surface spaced from the second active interior surface which has,in turn, bond pads thereon, including interconnection structure thereon,thereby forming a first portion of the gap defined between thesemiconductor device and the substrate. The substrate has an internalmetallized surface pattern of electrical circuits forming a secondportion of the gap, a thickness, and an external surface. A plurality ofthermal vias is formed between the internal metallized surface and theexternal surface of the substrate. Fill apparatus is provided forpositioning fill material proximate a portion of the gap about theperimeter thereof. A pressure chamber is positioned about the externalsurface of the semiconductor device being configured to apply fluidpressure about the perimeter of the gap and against the fill material tourge the fill material into the gap.

A vacuum chamber is also positioned about the external surface of thesubstrate. The vacuum chamber is configured to draw a vacuum in the gapthrough the thermal vias to urge the fill material into the gap.Additionally, pressure source apparatus is preferably connected to thepressure chamber to supply fluid (e.g., gas) under pressure and tomaintain such fluid at a desired pressure. A vacuum source is connectedto the vacuum chamber to draw a vacuum and to maintain the vacuum at aselected vacuum pressure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a simplified depiction of an apparatus used for practicing themethod of the present invention as well as a semiconductor device of thepresent invention;

FIG. 2 is an illustration of the exterior surface of a substrate of asemiconductor device involved in the present invention; and

FIG. 3 is a flow diagram illustrating the method of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to drawing FIG. 1, the apparatus as well as a semiconductordevice assembly 10 of the present invention is schematicallyillustrated.

A semiconductor device assembly 10 is shown having a semiconductordevice 12 spaced from a substrate 14 to define a gap 16 thereinbetween.As illustrated, the semiconductor device 12 includes a base 18 and asecond active interior surface 22 having bond pads 20 thereon. Thesemiconductor device 12 may be any suitable type flip chip semiconductordevice.

In FIG. 1, the second active interior surface 22 of the semiconductordevice 12 is shown opposite the exterior surface 24 of the base 18. Asshown, the second active interior surface 22 and exterior surface 24 arespaced apart, generally aligned, forming the base 18 having exteriorside wall 26. The base 18 may be of any suitable desired geometric shapeand thickness.

The bond pads 20 on the second active interior surface 22 of thesemiconductor device 12 may be formed in a variety of desiredconfigurations known to those in the art. The bond pads 20 may alsoinclude various interconnection structures for connection to themetallized surface pattern of electrical circuits 28 on interior surface40 of the substrate 14. The substrate 14 may be any acceptable substrateused for mounting and receiving a semiconductor device 12 comprised ofthe base 18 having bond pads 20 and interconnecting structure thereon,such as an FR-4 type substrate board.

As illustrated, the interconnecting structure comprises a plurality ofsolder bumps, such as solder bumps 34 and 36, which are positioned tocontact desired locations on the metallized surface pattern ofelectrical circuits 28 associated with interior surface 40 of substrate14 facing inwardly toward the gap 16.

The semiconductor device assembly 10, illustrated is a flip chipsemiconductor device, which includes a semiconductor chip 12 “flipped”to have its connective structure and, more particularly, the solderbumps 34 and 36 aligned with and attached to desired connecting pointsof the metallized surface pattern of electrical circuits 28 of thesubstrate 14. The solder bumps 34 and 36 are preferably flowed togetherusing any suitable type of heating for securing the semiconductor device12 to the metallized surface pattern of electrical circuits 28 of thesubstrate 14.

The substrate 14 also has an exterior surface 38 spaced from theinterior surface 40, and, more particularly, the metallized surfacepattern of electrical circuits 28, to provide a rigid substrate forsupporting the semiconductor device 12. Substrate 14 may be of anysuitable geometric configuration and thickness suitable for use with thesemiconductor device 12.

The substrate 30 is formed having a plurality of thermal vias, such asthermal vias 42, 44, 46, 48, 50 and 52. The thermal vias are formed in apredetermined configuration and in sufficient quantity, such as thoseillustrated in FIG. 2, to remove a predetermined amount of heat from thegap 16. More specifically, in FIG. 2, the substrate 30 is shown with aplurality of thermal vias in a predetermined pattern or matrix 54. Thenumber of thermal vias formed is selected based on the amount of heat,the nature of the circuit, the type of substrate, the type of circuitryon the substrate, and other such factors as known to those in the art.The thermal vias may be formed in any desired configuration necessary toeffect transfer of heat from the semiconductor device 12 and theconnection thereof to the substrate 14 and, more particularly, thetransfer of heat from the gap 16 to the exterior of the substrate 30.

As shown in FIG. 1, the thermal vias 42, 44, 46, 48, 50 and 52 each mayhave a separate metallized interior 56. The metallized interior 56 isused to facilitate heat transfer from the interior surface 40, themetallized surface pattern of electrical circuits 28, and the gap 16 tothe exterior of the substrate 14 of the semiconductor device assembly10. That is, each of the thermal vias, such as thermal via 42, may havethe interior thereof metallized, as shown at 56, to facilitate heattransfer.

The thermal vias such as vias 42, 44, 46, 48, 50 and 52, as well asthose appearing in the matrix 54 illustrated in drawing FIG. 2,preferably are cylindrical in shape having a diameter from about a 0.001inches to about 0.010 inches. The thermal vias 42, 44, 46, 48, 50 and52, as well as those in the matrix 54, are formed by well knownacceptable techniques.

In reference to FIG. 1, solder bumps 34 and 36 may be formed fromvarious types of solder and various alloys thereof, conductive polymer,other materials known in the art such as gold, indium, silver, platinumand various alloys thereof, any one of which are selected to facilitateflow or reflow thereof to make the desired electrical interconnections.

Also, as shown in FIG. 1, a fill material 60, referred to as anunderfill material, is shown positioned in the gap 16 between thesemiconductor device 12 and the substrate 14. That is, the fill material60 is positioned to seal the active surface 22 of the semiconductordevice 12, as well as the solder bumps 34 and 36 and the metallizedsurface pattern of electrical circuits 28. The fill material 60 may beselected to enhance the mechanical bond between the semiconductor device12 and the substrate 14, to help distribute stress on the semiconductordevice 12 and the solder bumps 34 and 36, and to increase structuralrigidity and, in turn, facilitate longer life and reduce damage fromphysical shock to the semiconductor device assembly 10. The fillmaterial 60 also helps protect the semiconductor device 12 and substrate14 from contaminants, including moisture, chemicals, chemical ions, andthe like.

The fill material 60 is typically a polymeric material, such as an epoxyor acrylic resin, that may contain various types of inert fillers. Thefill material 60 is typically selected to have a thermal coefficient ofexpansion that approximates that of the semiconductor device 12 and/orthe substrate 14 to help minimize the stress placed on the semiconductordevice assembly 10 and, more particularly, on the semiconductor device12 in relation to the substrate 14 in differing thermal conditions.

To promote filling the gap 16, the viscosity of the fill material 60 iscontrolled and selected to facilitate the flow thereof to the interior63 of the gap 16. That is, it is desirable for the fill material 60 toeasily and readily flow to fully fill the volume of the gap 16 whileminimizing voids, bubbles and non-uniform disposition of the fillmaterial in the gap 16.

For the semiconductor device assembly 10 of FIG. 1, a vacuum is providedproximate the thermal vias in order to draw material in and around thegap 16 to the exterior of the substrate 14. The vacuum urges the fillmaterial 60 from the gap perimeter 61 into the interior 63 of the gap 16to uniformly dispose fill material 60 throughout the gap 16, theperimeter 61 of the gap 16 being defined by the geometry of thesemiconductor device 12. As illustrated, in FIG. 1, the perimeterextends around all sides of the semiconductor device 12. If desired, thefill material may be provided about a portion of the perimeter 61,rather than the entire perimeter 61.

As illustrated in FIG. 1, apparatus may be provided to facilitateconstruction of the desired semiconductor device assembly 10. Asillustrated, the apparatus is shown in simplified form with a support64, configured to receive and support a semiconductor device assembly 10thereon. For example, semiconductor device assembly 10 may be placed onthe support 64 and supported by a sealing device 68 to minimize leakageof fluids thereby, such as air. All, or a portion of the thermal vias42, 44, 46, 48, 50 and 52, or alternatatively, at least a portion of thethermal vias of the matrix 54 shown in FIG. 2, are exposed or uncoveredand face into a vacuum chamber 66.

As here shown, the vacuum chamber 66 is formed by an exterior wall 70,which may be domed, rectangular or in any convenient desired shape.

The vacuum chamber 66 has an evacuation line 72 interconnected throughthe exterior wall 70. A vacuum valve 74 is interconnected in theevacuation line 72 to interconnect the vacuum chamber 66 with a vacuumsource 76.

The vacuum source 76 may be of any convenient type of industrial vacuumsource. For instance, it may be a simple vacuum pump designed orconfigured to draw a vacuum (e.g., one or more atmospheres) tofacilitate the flow of the fill material 60 from the perimeter 61 to theinterior 63 of the gap 16 without imposing undesired stress on thesubstrate 30 and the semiconductor device 12. However, a vacuum valve 74is provided and may be used to isolate the vacuum chamber 66 from thevacuum source 76. A bleed valve 78 is provided interconnected into theevacuation line 72 to allow the vacuum to be relieved therethrough.

It must be stated that the term “vacuum” as used herein, is used todescribe the removal of gas or other matter from the vacuum chamber 66to create a negative pressure, i.e., a pressure, less than atmosphericpressure within the vacuum chamber 66.

A pressure chamber 80 is formed by a sidewall 82, which may be, ifdesired, connected to the exterior wall 70, forming the vacuum chamber.The sidewall 82 may be formed in any particular desired shape, includinghemispheric, rectilinear or the like, to create a chamber into which afluid pressure may be exerted as hereinafter described.

As illustrated in FIG. 1, the sidewall 82 of the pressure chamber 80 isan extension of the exterior wall 70 of the vacuum chamber 66 since bothmay be unitarily formed with the support 64, thereby resulting in thepressure chamber 80 and the vacuum chamber 66 all being a singlestructure. As illustrated, the pressure chamber 80 includes a lid 84,secured by a hinge 86, and held closed by a latch 81. When closed, thelid 84 is sealed by an o-ring 90. Other types of suitable sealconfigurations may be used to provide a sealing relationship for the lid84, as desired.

The lid 84 is sized to facilitate positioning and removal of asemiconductor device assembly 10 into and out of pressure chamber 80, asillustrated. With the lid 84 secured as illustrated in FIG. 1, pressuremay be supplied by a pressure source 92, such as a small compressor or asource of pressurized gas, through a pressure line 94 and a pressureisolation valve 96. Pressure, particularly using a suitable gas, is usedto provide a forces 98 and 100 against the fill material 60 positionedproximate the perimeter 61 of the gap 16 to urge the fill material 60toward the interior 63 of the gap 16. Thus, it can be seen that adifferential pressure is created between the pressures 98, 100 appliedin the pressure chamber 80 and the vacuum 62 drawn in the interior 63 ofthe gap 16 through thermal vias 46, 48 by way of the vacuum chamber 66.In view of the differential pressure, the applied vacuum pressure forcewhich urges the fill material 60 toward the interior 63 of the gap 16and is enhanced so that fill material may be selected to reduce cost,enhance strength, and facilitate complete filling of the gap 16.Further, the evacuation of the interior 63 of the gap 16 eliminates theneed to provide a way for trapped air to escape upon movement of fillmaterial 60 toward the interior 63. Also it is believed that the use ofa vacuum to fill the gap 16 helps reduce the number of bubbles in thefill material 60 and helps provide a more uniform distribution of fillmaterial 60 in the gap 16.

In referring to the pressure chamber 80, it may be noted that a bleedvalve 106 is provided to vent the pressure that is built up to theinterior of the pressure chamber 80 upon operation of the pressuresource 92 and positioning the valve 96 in the open position. That is,the pressure in chamber 80 may be relieved before opening the lid 84.

It may be noted that the valves 106, 96, 78 and 74 are here shown insimplified schematic form with an open circle representing a valve in anopen position and with a circle having a cross through representing avalve in a closed position. Any suitable desired valve may be usedconsistent with the pressures being used.

It may be noted that the source of pressure may provide air, gas, or anyother suitable fluid to apply pressure. In practice, it may be desiredto use inert gas, including, for example, dry nitrogen.

Referring to drawing FIG. 3, to practice a method of making asemiconductor device assembly 10 using the disclosed apparatus, asemiconductor device 12 and a substrate 14, as shown in blocks 120 and122, are positioned relative to each other, as illustrated in FIG. 1.The semiconductor device 12 is connected at 124 to the substrate 14,preferably by reflowing the solder bumps 34 and 36. The substrate 14 andthe semiconductor device 12 are then supported on the support 64engaging sealing device 68, the semiconductor device 12 connected to thesubstrate 14 defining a gap 16 to be filled. On the perimeter 61 of thegap 16, a fill material 60 is positioned by a filling device 110, asillustrated in FIG. 1 to be a cylinder 112 with a piston 114 operable tourge fill material 116 outward through applicator tube 118. Otherstructures or devices may be used to position the fill material 60 aboutthe perimeter 61 as desired.

The fill material 60 is preferably positioned, as indicated at 126,about the perimeter 61 prior to placement in the pressure chamber 80proximate the vacuum chamber 66. However, in some situations it may beappropriate to apply the fill material after the semiconductor device 12and substrate 14 are connected and positioned on the support 64.

After positioning the semiconductor device 12 and substrate 14 asrepresented by blocks 120 and 122 on the support 64, when they areconnected as shown by block 124, thereafter, a vacuum 62 may be drawn128 in vacuum chamber 66 by operation of valves 74, 78 and the vacuumsource 76. That is, the gas or air in the vacuum chamber 66 and in thegap 16 may be evacuated through the evacuation line 72 to create avacuum, pressure less than atmospheric pressure, within the vacuumchamber 66 and in the gap 16. Either simultaneously or sequentially, butpreferably substantially simultaneously, a pressure is applied 130 fromthe pressure source 92 through the pressure line 94 and valve 96 to thepressure chamber 80. The pressure applies a force illustrated in phantomby arrows 98 and 100, as illustrated in drawing FIG. 1, against the fillmaterial 60 to help urge the fill material towards the interior 63 ofthe gap 16. After the pressures 98 and 100 have been applied and thevacuum 62 has been applied to the exterior surface 38 and, moreparticularly, through the thermal vias 42, 44, 46, 48, 50 and 52 to theinterior 63 of the gap 16 for a selected period of time determined byexperimentation for the selected fill material, the valves 74 and 96 areclosed and the bleed valves 106 and 78 are opened to relieve the vacuum62 and to release the pressure within the respective vacuum chamber 66and pressure chamber 80, as illustrated by blocks 132 and 134.Thereafter, the lid 84 is opened and the semiconductor device assembly10 removed as illustrated by block 136.

While the present invention has been described in terms of certainmethods, embodiments and apparatus, it should not be construed to be solimited. Those of ordinary skill in the art will readily recognize andappreciate that additions, deletions and modifications to theembodiments described herein may be made without departing from thescope of the invention as hereinafter defined.

What is claimed is:
 1. A method of flowing a material into a portion ofa semiconductor device assembly having a semiconductor die having afirst surface and a second active surface having connectors thereon to asubstrate having a first surface pattern of electrical circuits forcontacting with said connectors of said semiconductor die, saidsubstrate having an exterior surface spaced from said first surfacepattern of electrical circuits and a plurality of vias extending throughsaid first surface pattern of electrical circuits to said exteriorsurface, said method of connecting using a source of pressure and vacuumin a chamber comprising: connecting said connectors of saidsemiconductor die to a portion of said substrate having said connectorscontacting a portion of the first surface pattern of electrical circuitsof said substrate, said connectors forming a gap having a perimeter;placing fill material proximate the perimeter of said gap; and actuatingsaid source of vacuum and said source of pressure for urging said fillmaterial into said gap using said vacuum through one via of saidplurality of vias and said pressure about said perimeter.
 2. The methodof claim 1, wherein said connectors includes a plurality of bumps.
 3. Amethod of flowing a backfill material for backfilling a flip-chip gap ina chamber having a source of pressure and a source of vacuum connectedthereto, said gap formed between a flip chip semiconductor die havingconnectors thereon mounted on a substrate, said gap having a perimeter,said substrate having a plurality of vias formed therein extendingbetween said gap and an external surface of said substrate, said methodcomprising: positioning a fill material about the perimeter of said gap;and actuating said source of pressure and said source of vacuum, saidpressure for creating a pressure in said pressure chamber for urgingsaid fill material into said gap and said source of vacuum for drawing avacuum through said plurality of vias for urging said fill material intosaid gap.
 4. A method of flowing a material into a flip-chip gap in achamber having a source of pressure and a source of vacuum connectedthereto and having a support located therein, said gap formed in aflip-chip semiconductor device assembly including a flip chipsemiconductor die having connectors thereon connected to a portion of asubstrate for defining said gap having a perimeter, said substratehaving a plurality of vias formed therein for extending between said gapand an external surface of said substrate, said support for supportingsaid substrate thereon, said method comprising: positioning a fillmaterial about the perimeter of said gap; and operating said source ofvacuum for drawing a vacuum in a portion of said vacuum chamber and insaid gap through said plurality of vias for urging said fill materialinto said gap while operating said source of pressure for a pressure toact on said fill material for urging said fill material into said gap.